The isolated susceptibility χI may be defined as a (non-thermodynamic) average over the canonical ensemble, but while it has often been discussed in the literature, it has not been clearly measured. Here, we demonstrate an unambiguous measurement of χI at avoided nuclear-electronic level crossings in a dilute spin ice system, containing well-separated holmium ions. We show that χI quantifies the superposition of quasi-classical spin states at these points, and is a direct measure of state concurrence and populations.
@article{arxiv.2102.11969,
title = {Experimental measurement of the isolated magnetic susceptibility},
author = {D. Billington and C. Paulsen and E. Lhotel and J. Cannon and E. Riordan and M. Salman and G. Klemencic and C. Cafolla-Ward and D. Prabhakaran and S. R. Giblin and S. T. Bramwell},
journal= {arXiv preprint arXiv:2102.11969},
year = {2021}
}